1. Technical Field of the Invention
This invention relates to amine terminated polyamides. More particularly, this invention relates to amine terminated polyamides having an average molecular weight of about 3,000 to about 10,000 which are useful in the preparation of adhesives, elastomers, polyamide-polyurea foams, polyepoxides, polyimides, etc.
Still more particularly, this invention is related to the preparation of normally liquid amine terminated polyamides having a molecular weight within the range of about 3,000 to about 10,000 and to a method for the preparation of such amine terminated polyamides by the reaction of an aromatic or an aliphatic dicarboxylic acid with a first higher molecular weight polyoxypropylene diamine and with a second lower molecular weight polyoxypropylene diamine.
2. Prior Art
It is known, as exemplified by Yeakey U.S. Pat. No. 3,654,370 to prepare polyoxyalkylene polyamines by the reductive amination of a polyoxyalkylene polyol. The reductive amination is conducted catalytically in the presence of hydrogen and ammonia and an appropriate reductive amination catalyst, such as a nickel, copper and chromia catalyst. The polyoxyalkylene polyamines that are prepared in this fashion are stable articles of commerce having a wide variety of uses such as those mentioned above. In particular, they have found utility as curing agents for epoxy resins, as plasticizers, as cross linking agents and binders for textiles, and as intermediates in the preparation of polyureas. In general, polyoxyalkylene polyamines having molecular weights ranging from about 200 to about 5,000 can be prepared by the Yeakey process.
Klein U.S. Pat. No. 4,133,803 discloses thermoplastic adhesives having a melting point between 20.degree. C. and 180.degree. C. prepared from polyoxypropylene diamines and triamines and mixtures thereof having molecular weights of about 190 to about 3,000 and aliphatic or aromatic dicarboxylic acids, esters and anhydrides thereof containing about 2 to 30 carbon atoms per molecule. The polyoxypropylene amine component and the dicarboxylic acid component are reacted in the mole ratio of about 0.25:1 to about 4.0:1. The thermoplastic adhesives of Klein are useful in the preparation of "hot melt" adhesives. In Example I, a thermoplastic adhesive prepared by reacting a molar excess of a polyoxypropylene diamine having an average molecular weight of about 230 with isophthatic resin at a temperature of 200.degree.-240.degree. C. was formulated at 140.degree. C. with an epoxy resin, a plasticizer and silica to provide adhesives that were applied to substrates with good results.
Yeakey et al. U.S. Pat. Nos. 4,128,525 and 4,182,845 are directed to thermoplastic adhesives of the type disclosed in Klein U.S. Pat. No. 4,133,803 modified by the inclusion of piperazine together with the polyoxypropylene diamine or triame as a reactant, the piperazine constituting at least 80 mole percent of the amine component.
In Kuceski U.S. Pat. No. 4,182,844 an energy-conserving method is disclosed for use in the manufacture of polyaminoamides of the type prepared by reacting a polycarboxylate ester with a mono- or polyalkylene polyamine wherein the reactants are externally heated only to a temperature (e.g. 125.degree. C.) at which the exothermic reaction becomes self-sustaining, after which external heating is discontinued. The desired temperature range is thereafter maintained because the heat of reaction is used to vaporize by-product water and alcohol from the reaction mixture.
Impact resistant thermoplastic polyamides useful in the preparation of holt melt adhesive formulations by interreacting 57.5-94.75 mole percent of a short chain polyamide forming moiety such as a dicarboxylic acid or a diamine with 5-30 mole percent of a polyamide-forming dimer acid moiety and 0.25-12.5 mole percent of a polyamide-forming moiety such as an amine or carboxy terminated butadiene-acrylonitrile copolymers or poly(oxyalkylene) diamines.
Bentley et al. U.S. Pat. No. 4,751,255 relates to polymeric polyamines having molecular weights ranging from 1,000 to 16,000 and containing from 2 to 4 primary amino groups per molecule which are prepared by reacting a polycarboxylic acid or ester with a stoichiometric excess of a polyamine having terminal aminopropoxy groups and a molecular weight of less than 500. In an example, a molecular excess of a polyoxypropylene diamine having an average molecular weight of about 400 was reacted with dimethyl terephthalate to provide a product having a viscosity of 931 centistokes at 100.degree. C.
3. Background of the Invention
The polyoxyalkylene polyamines of the type disclosed in Yeakey U.S. Pat. No. 3,654,370 are prepared from polyols prepared by the oxyalkylation of a polyhydric alcohol. The preferred starting materials are dihydric and trihydric alcohols such as propylene glycol or glycerol and propylene oxide or ethylene oxide. Copolymer polyols of ethylene oxide and propylene oxide are also useful, particularly those containing from about 5 to about 40 wt. % of ethylene oxide and, correspondingly, from about 95 to about 60 wt. % of propylene oxide.
The molecular weight of the polyol is determined by the number of moles of epoxide that are reacted with the alcohol initiator. Since the addition is random, the final alkoxylation product will not be a pure compound but, rather, will be a mixture of polyoxyalkylene polyols For example, if the polyol is a polyol prepared by reacting glycerol or trimethylol propane with propylene oxide, using an amount of propylene oxide adequate to provide for an average molecular weight of about 1,000, the final propoxylation product will actually be composed of a mixture of polyoxypropylene triols having molecular weights varying from about 800 to about 1,200, the molecular weight distribution following a Gaussian distribution curve (sometimes referred to as a sine curve or a Poissan curve). As the molecular weight of the polyol increases, the spread in the molecular weights will also increase. Thus, when the average molecular weight of the triol is about 3,000, the deviation will be about .+-.400 molecular weight units so that most of the product will fall within the molecular weight range of about 2,600 to about 3,400.
As the molecular weight is still further increased, the percentage of free hydroxyl groups in the reaction mixture will decrease because of the added bulk of the already formed polyol, thus making the addition of more propylene oxide groups progressively more difficult. As a practical matter, when the triol reaches an average molecular weight of about 5,000, further propoxylation is accomplished only with extreme difficulty. The 5,000 molecular weight polyoxypropylene triols will have a molecular weight distribution of about .+-.000 so that the actual molecular weight range will be from about 4,000 to about 6,000. Again, the molecular weight distribution following a Gaussian distribution curve.
A further complication is encountered during the propoxylation to the higher molecular weights. As the reaction time and temperature are increased to encourage propoxylation, there is introduced a tendency on the part of the propylene oxide to isomerize to allyl alcohol and a tendency on the part of the hydroxypropyl end groups of the polyoxypropylene triol to dehydrate to form a terminal olefin group and water. Both the water and the allyl alcohol are susceptible to oxyalkylation thereby diluting the polyoxypropylene diol with undesired generally low molecular weight diol contaminants derived from the water and monofunctional allyl alcohol propoxylates. From as little as one percent to as much as ten percent of the oxypropyl end groups of the triol may dehydrate to form groups with terminal unsaturation in increasing the average molecular weight from about 3,000 to about 5,000.
When a polyoxypropylene polyol of this nature is reductively aminated in accordance with the procedure of Yeakey U.S. Pat. No. 3,654,370, comparatively higher temperatures and longer reaction times are required as the molecular weight of the polyol increases This can result in the cleavage of the polyol to form undesired and unwanted alkyl ether by-products and hydrogenation of the unsaturated groups on the polyol to form propyl ethers.
Thus, although the results obtained heretofore with polyoxyalkylene diamines and triamines of the type disclosed by Yeakey have been generally satisfactory, problems such as those mentioned above have detracted from the utility of the products.
It is known to use polyamides as hot melt adhesives. They are used as hot melt adhesives because the polyamides are normally high melting solids or resinous materials which are not liquids at ambient temperatures. It is believed that these characteristics are brought about because of the hydrogen bonding that occurs throughout the amide linkages.
Polyamides prepared by reacting a molar excess of a low molecular weight polyoxypropylene diamine having a molecular weight of about 150 to about 700 with an aliphatic dicarboxylic acid such as adipic acid are not pourable at room temperature and are very viscous even at 60.degree. C. In addition, these products are not compatible with high molecular weight polyether polyols or polyether amines and are therefore of only marginal utility in the preparation of polyurethanes.